From owner-freebsd-chat Fri Feb 25 21:33:32 2000 Delivered-To: freebsd-chat@freebsd.org Received: from cc942873-a.ewndsr1.nj.home.com (cc942873-a.ewndsr1.nj.home.com [24.2.89.207]) by hub.freebsd.org (Postfix) with ESMTP id 4CDD837BC5C for ; Fri, 25 Feb 2000 21:33:28 -0800 (PST) (envelope-from cjc@cc942873-a.ewndsr1.nj.home.com) Received: (from cjc@localhost) by cc942873-a.ewndsr1.nj.home.com (8.9.3/8.9.3) id AAA20895; Sat, 26 Feb 2000 00:37:41 -0500 (EST) (envelope-from cjc) Date: Sat, 26 Feb 2000 00:37:41 -0500 From: "Crist J. Clark" To: Alfred Perlstein Cc: cjclark@home.com, Marco Molteni , freebsd-chat@FreeBSD.ORG Subject: Re: how to do this C preprocessor trick? Message-ID: <20000226003741.C20702@cc942873-a.ewndsr1.nj.home.com> Reply-To: cjclark@home.com References: <20000225182432.A5017@sofia.csl.sri.com> <20000226001121.A20702@cc942873-a.ewndsr1.nj.home.com> <20000225214616.U21720@fw.wintelcom.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 1.0i In-Reply-To: <20000225214616.U21720@fw.wintelcom.net>; from bright@wintelcom.net on Fri, Feb 25, 2000 at 09:46:17PM -0800 Sender: owner-freebsd-chat@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org On Fri, Feb 25, 2000 at 09:46:17PM -0800, Alfred Perlstein wrote: > * Crist J. Clark [000225 21:36] wrote: > > On Fri, Feb 25, 2000 at 06:24:32PM -0800, Marco Molteni wrote: > > > Hi all, > > > > > > I have a function that takes a variable number of arguments: > > > > > > void d_printf(const char *format, ...) > > > > > > I would like to make it print automatically the function name > > > from which it is called, eg instead of doing > > > > > > f() { d_printf("f: blabla", x, y, z); } > > > > > > doing simply > > > > > > f() { d_printf("blabla", x, y, z); } > > > > > > To do that, I though of wrapping d_printf() around a macro like > > > > > > #define dprintf(x) d_printf(__FUNCTION__, x) > > > > > > but whatever combination I use (also with #), the thing is not going to work: > > > > > > main.c:231: macro `d_printf' used with too many (4) args > > > > > > Is it possible to trick the C preprocessor to do what I want? > > > > Yeah, I use the same type of thing to produce error messages. I'm > > having a little bit of trouble understanding exactly what you are > > trying to do above, so I'll just show my solution to my problem. > > > > I wanted to just be able to do, > > > > errmsg(char fmt, ...) > > > > But have it print, > > > > cmd(file:line)- Error message > > > > Where 'cmd' is the name of the program (the tail of argv[0]), 'file' > > is the C source file name, and 'num' is the line number. > > > > char *cmd > > > > void _errmsg(char *fmt, ... ) > > { > > va_list ap; > > > > va_start(ap,fmt); > > vfprintf(stderr,fmt,ap); > > va_end(ap); > > } > > > > #define errmsg fprintf(stderr,"%s(%s:%d)- ",cmd,__FILE__,__LINE__); _errmsg > > > > > > Gets me around the varargs in the precompiler by not using _any_ > > args in the macro. So, > > > > errmsg("cannot fine file: %s\n",str); > > > > Expands to, > > > > fprintf(stderr,"%s(%s:%d)- ",cmd,__FILE__,__LINE__); _errmsg("cannot fine file: %s\n",str); > > > > And you know, it works. Big help in debugging big apps. When it's sent > > bound for users, I make the messages a bit less verbose, but only > > takes the one change. > > One of the nasty side effects is that this makes the macro expand to > multiple statements. > > what's so bad about that? > > if (foo < 0) > errmsg("foo < 0"); > > Macros that expand to multiple statements ought to be enclosed in a > do { } while(0) loop. > > Although the extra parens are ugly, it things a bit safer/cleaner. Why a, do { } while(0) Rather than just, { } That's how I group multi-statement macros, but that does not work for this one. I just saw your answer and I guess it boils down to which is more ugly and which is easier to forget to do properly, Yours, d_printf((fmt,arg1,arg2)); Or mine, { d_printf(fmt,arg1,arg2); } Extra pair of parenthesis or extra pair of curly brackets? ;) Or am I overlooking another vulnerability? -- Crist J. Clark cjclark@home.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-chat" in the body of the message